1. Technical Field
This disclosure relates generally to a sealing system for use in a gas turbine engine and, more particularly, to a distortion resistant face seal counterface system for use in a gas turbine engine.
2. Background Information
A typical prior art mechanical face seal arrangement within a gas turbine engine (sometimes referred to as a carbon face seal arrangement) includes a stationary seal member disposed in contact with, and sealing against, a rotating seal counterface (also referred to as the seal plate). The counterface is locked into place relative to a rotating engine shaft by an axially directed compressive force that may, depending upon the application, be several thousands of pounds in magnitude. In some applications, the compressive force is applied non-uniformly around the circumference of the shaft. As a result, the seal counterface may warp and assume a “wavy” configuration wherein the seal surface of the counterface is not planar; i.e., the axial position of the seal surface varies as a function of circumferential position.
It is known that rubbing between the counterface and the stationary seal member can generate significant amounts of heat, and consequent thermal gradients within the counterface. The thermal gradient forms because the surface (i.e., the seal surface) of the counterface in contact with the seal member rises to a much higher temperature during operation, than an aft surface on the opposite side of the counterface. The portion of the counterface proximate the seal surface will, as a result, experience greater thermal expansion than the aft surface. The difference in thermal expansion causes the seal surface to diverge from its original planar orientation, away from the stationary seal member, resulting in the counterface assuming a cone-like geometry. This deformation is typically referred to as “coning”. Coning can create an undesirable gas leakage path between the seal surface of the seal counterface and the seal member. Coning can also lead to excessive wear of the members that are in running contact.
One prior art approach to preventing the deformation of the counterface caused by coning has been to provide external or internal cooling of the counterface in the form of oil jets, cooling fins, or cooling passages. However, this approach adds significant complexity to the design of the counterface and is expensive. Another approach to preventing the deformation of the counterface has been to make the counterface from a ceramic. However, ceramics may cause other problems due to their brittleness.